我想从Parse中检索用户分数并将其分配给变量。此函数在查询完成之前返回0。我在Retrieve object from parse.com and wait with return until data is retrieved找到了类似的答案。但是,我希望函数有一个返回值,并且在调用此函数时我应该使用什么参数作为completionhandler。任何帮助将不胜感激,谢谢!
这是我的代码
func loadCurrentUserData() -> Int {
let query = PFQuery(className: "userScore")
let userId = PFUser.currentUser()!
var currentUserScore: Int = 0
query.whereKey("user", equalTo: userId)
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
if error == nil {
let scoreReceived = objects![0]["score"] as! Int
currentUserScore = scoreReceived
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.userScore.text = "\(scoreReceived)"
})
} else {
print("Error: \(error!) \(error!.userInfo)")
}
}
return currentUserScore
}
答案 0 :(得分:3)
设置此功能的方式不起作用,因为查询方法是异步的。这可以通过两种方式解决:
1)使用PFQuery同步类别: http://parse.com/docs/ios/api/Categories/PFQuery(Synchronous).html
这种方法的唯一缺点是该方法将变为阻塞,因此请务必从后台线程调用它。
2)重构函数以使用完成块而不是返回值.i.e:
func loadCurrentUserData(completion: (score: Int!, error: NSError?) ->()) {
let query = PFQuery(className: "userScore")
let userId = PFUser.currentUser()!
var currentUserScore: Int = 0
query.whereKey("user", equalTo: userId)
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
if error == nil {
let scoreReceived = objects![0]["score"] as! Int
currentUserScore = scoreReceived
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.userScore.text = "\(scoreReceived)"
})
completion(score: currentUserScore, error: nil);
} else {
print("Error: \(error!) \(error!.userInfo)")
}
completion(score: currentUserScore, error: error);
}
}